Method for lowering the air temperature of an engine compartment of a vehicle

ABSTRACT

In a method for lowering the air temperature of an engine compartment of a vehicle accommodating an internal combustion engine, an air-fluid heat exchanger having at least one cooling element for cooling the air-fluid heat exchanger, and an electric drive, the at least one cooling element is activated as a function of the temperature of a fluid side of the air-fluid heat exchanger and as a function of a temperature of the electric drive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an electronic control device for lowering the air temperature of an engine compartment of a vehicle.

2. Description of the Related Art

The importance of systems for reducing fuel consumption and thus CO₂ emissions by vehicles has been increasing steadily during the public discussion of CO₂ and in view of the steady rise in fuel prices.

Against this background, hybridization of vehicle drive trains has become increasingly important. So-called hybrid vehicles are known from the related art which have, in addition to a conventional internal combustion engine, a second power source, typically an electric drive having a drive voltage of more than 100 V.

One goal of hybrid vehicles which also have an electric machine in addition to a conventional internal combustion engine is the recovery (recuperation) of kinetic energy released during a braking operation and the potential energy released during a downhill drive. This energy may be utilized after being converted into an electrical form in order to supply the vehicle electrical system, which has a definite influence on the vehicle's fuel consumption.

If the electric machine also allows motor operation through an inverter, a drive torque of the internal combustion engine may be increased by an electrical torque (“boosted”) to increase driving performance, for example. Furthermore, if more energy is recovered through recuperation than is needed for the power supply of the vehicle electrical system and the “boost” function, then there is also the possibility of reducing the drive torque of the internal combustion engine in a targeted manner and compensating for it by an electrical torque. Due to this shift in load point of the internal combustion engine, a further reduction in fuel consumption may be achieved.

However, other functions must also be ensured in addition to the functions mentioned above. For example, a reliable power supply of the vehicle electrical system even during prolonged standing phases with an idling engine (e.g., in a traffic jam situation) must also be ensured.

In today's vehicles, the goal is to operate the engine with relatively high coolant temperatures from the standpoint of efficiency. A fan in a conventional air-fluid heat exchanger is therefore activated only at the highest possible coolant temperatures. The air temperature in the engine compartment plays little or only a subordinate role in considerations about controlling the fan.

The result of this measure is that the air temperature level in the engine compartment continues to rise and temperatures significantly above 100° C. may occur there, even if the temperature on the fluid side of the air-fluid heat exchanger is around 100° C. or less.

In today's hybrid vehicles, mainly a combination of a water-cooled inverter with an electric machine is used as the electric drive. For cost reasons, however, it is desirable to provide air cooling for the electric drive as an attractive alternative.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is a method for lowering the air temperature of the engine compartment of a vehicle which is provided for holding an internal combustion engine, an air-fluid heat exchanger having at least one cooling element for cooling the air-fluid heat exchanger and an electric drive, the at least one cooling element being activated as a function of a temperature of a fluid side of the air-fluid heat exchanger and as a function of a temperature of the electric drive.

The term “cooling element” in this context should be understood in particular to refer to passive cooling elements which permit a supply of a fluid provided for cooling in a passive manner. In addition, however, active cooling elements should also be included, which actively convey the fluid provided for cooling itself. The fluid is preferably the ambient air of the vehicle.

In this way, ambient air at a sufficiently low temperature level may be made available for cooling the electric drive without any negative effect on the optimized cooling strategy for the internal combustion engine.

Furthermore, it is proposed that the at least one cooling element should be formed by a fan. Therefore the effort for making available the ambient air at a sufficiently low temperature level may be minimized because a fan is standard equipment in vehicles having the features described here.

Furthermore, it is proposed that in the method according to the present invention, a second cooling element is used which is formed by at least one flap, this flap being adjusted by activation from a first position, in which an access of ambient air from outside the engine compartment through the flap into the engine compartment is prevented, into at least a second position in which the access of ambient air from outside the engine compartment into the engine compartment is made possible through an opening formed by the flap, the at least one flap being reversibly adjustable between the first position and the second position. In this way, ambient air at a lower temperature level may be made available in a particularly simple manner for lowering the air temperature of the engine compartment while the vehicle is moving in a forward direction.

If the electric drive is operated in a nominal operating range at an electrical voltage of at most 60 V, then demands for protection against electrical shock and the associated effort may be reduced due to the low electrical voltage, and at the same time a particularly high controlled motor power may be achieved with the help of the method since electrical losses on the usual semiconductor elements of a motor power controller and on windings of the electric drive increase quadratically with an electrical current flowing through the semiconductor components and the windings.

It is also proposed that in the method according to the present invention the electric drive includes an inverter through which motor operation of the electric drive is made possible. In this way, a drive torque of the internal combustion engine may be increased (“boosted”) by an electrical torque to increase the technical driving properties of the vehicle. In a suitable embodiment in which more energy is recovered through a recuperative method than is needed to supply the vehicle electrical system and the “boost” function, there is also the possibility of reducing a nominal mechanical drive torque of the internal combustion engine and compensating for it by the electrical torque. A further reduction in fuel consumption by the vehicle is achievable through this shift of the load point.

It is also proposed that the air temperature of the engine compartment should be adjusted by activating at least one cooling element in an electronic control circuit or regulating circuit to a setpoint temperature range. A particularly uniform lowering of the air temperature of the engine compartment and a particularly effective cooling of the electric drive may be achieved in this way. A predetermined maximum limiting value of the air temperature of the engine compartment preferably amounts to at most 90° C. In this way, an air temperature having a particularly high temperature difference with respect to the electric drive may be made available, which may permit particularly effective cooling of the electric drive.

Another object of the present invention is an electronic control device for at least lowering the air temperature of the engine compartment of a vehicle which is provided for holding an internal combustion engine, an air-fluid heat exchanger having at least one cooling element for cooling the air-fluid heat exchanger and an electric drive of the vehicle. The control device includes a control unit which is provided to activate the at least one cooling element independently of the temperature of the fluid side of the air-fluid heat exchanger and as a function of a temperature of the electric drive.

In an advantageous embodiment, the electronic control device includes a software module for controlling the control device according to at least one of the described methods, the at least one method being converted into a programming code of the software module which is implementable in the control unit and is executable by the control unit in order to lower the air temperature of the engine compartment of the vehicle. In this way, a flexible design of the control of the control device may be achieved.

If the control unit includes at least one electronic control circuit or regulating circuit which is provided for activating and deactivating the at least one cooling element in succession to adjust the air temperature of the engine compartment to a setpoint temperature range, a particularly uniform lowering of the air temperature of the engine compartment and particularly efficient cooling of the electric drive may be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a vehicle electrical system of a vehicle designed as a hybrid vehicle.

FIG. 2 shows a schematic diagram of an engine compartment of the vehicle having components accommodated therein.

FIG. 3 shows a flow chart of an embodiment of the method according to the present invention for lowering the air temperature of the engine compartment according to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic diagram of a vehicle electrical system 26 of a vehicle which is designed as a hybrid vehicle but is not shown in further detail here. Vehicle electrical system 26, which contains a conventional lead battery 28, includes a first voltage level of 14 V (right part of FIG. 1) which is provided for supplying first electrical consumers 30 and an optional starter 64. Furthermore, vehicle electrical system 26 has a second voltage level of 48 V for supplying second electrical consumers 34 using a high-performance battery 32 and an electric drive 36 (left part of FIG. 1), which includes an electric motor and an inverter. Electric drive 36 is therefore operated in a nominal operating range with an electrical voltage of max. 48 V.

A d.c./d.c. converter 38 of vehicle electrical system 26 is provided in a known way for adapting the supply voltage of the second voltage level to the supply voltage of the first voltage level.

The second voltage level is also used to ensure the power supply for vehicle electrical system 26 even during prolonged standing phases of the vehicle with an idling engine, for example, in a traffic jam situation.

Electric drive 36 is provided for utilizing, by recovery (recuperation), the kinetic energy released during a braking operation or the potential energy released during a downhill drive after conversion into an electrical form to supply vehicle electrical system 26 and to significantly reduce the fuel consumption of the vehicle.

The inverter permits motor operation of electric drive 36, so that in addition to a conventional drive torque, an electric drive torque (“boost”) may be generated to increase the driving performance of the vehicle.

Electric drive 36 has a first temperature sensor 48 (FIG. 2) mounted at a location on electric drive 36 where experience has shown the greatest heating occurs during operation of electric drive 36.

FIG. 2 shows an engine compartment 12 of the vehicle in schematic form. Engine compartment 12 is provided for holding

-   -   an internal combustion engine 14 including a connected         transmission 16,     -   an air-fluid heat exchanger 18 having a first cooling element 20         formed by a fan to cool air-fluid heat exchanger 18,     -   an electric drive 36 and     -   an electronic control device 40.

Electronic control device 40 has a control unit 42 having a software module 46, which is used for controlling electronic control device 40 and has a second temperature sensor 50 with which air temperature T_(L) of the engine compartment may be determined.

Furthermore, electronic control device 40 is equipped with an input for connection of first temperature sensor 48 to ascertain temperature T_(EA) of electric drive 36.

Air-fluid heat exchanger 18 is provided in a known way for dissipating waste heat generated by internal combustion engine 14 into ambient air 24. Those skilled in the art are familiar with its functionality, which therefore need not be explained further below.

Viewed in the direction of a normal travel direction 10, engine compartment 12 is equipped with second cooling elements 22 formed by flaps in front of and behind a radiator grill. The flaps are adjustable by activation from a first position, in which an access of ambient air 24 from outside of engine compartment 12 through the flap into engine compartment 12 is prevented, into a second position, in which the access of ambient air 24 from outside of engine compartment 12 into engine compartment 12 through an opening formed by the flap is made possible.

The inverter of electric drive 36 has a number of semiconductor elements formed by bipolar transistors having an insulated gate electrode (IGBT, “insulated-gate bipolar transistors”). The semiconductor elements may fundamentally also be formed by MOSFETs or other semiconductor elements which appear suitable to those skilled in the art. To maintain full functional efficiency of these semiconductor elements, specific temperature limits must be maintained. For this reason, a first limiting value of 90° C. is predetermined for maximum air temperature T_(L) ^(max) of engine compartment 12, which is not to be exceeded in all driving situations. According to this embodiment, electric drive 36 is adequately cooled at this maximum air temperature T_(L) ^(max) of engine compartment 12.

First limiting value T_(L) ^(max) for air temperature T_(L) of engine compartment 12 is stored in a memory unit 44 of control unit 42. Furthermore, a second limiting value T_(L) ^(min) of 70° C. for a minimum air temperature T_(L) of engine compartment 12 is stored in memory unit 44 of control unit 42. Limiting value T_(L) ^(min) for minimum air temperature T_(L) of engine compartment 12 of 70° C. ensures that excessive dissipation of heat from internal combustion engine 14 may be avoided to be able to operate it in an optimum efficiency range.

In addition, a third limiting value T_(EA) ^(max) for a maximum temperature T_(EA) of electric drive 36 is also stored in memory unit 44 of control unit 42.

Electronic control device 40 is used to at least lower air temperature T_(L) of engine compartment 12 of the vehicle. For lowering air temperature T_(L) of engine compartment 12 of the vehicle, a method which is described below is provided.

This method includes method steps 52 through 62 (FIG. 3), which are converted into a program code of software module 46, which is implementable in control unit 42 of electronic control device 40 and is executable by control unit 42 to lower air temperature T_(L) of engine compartment 12 of the vehicle.

FIG. 3 shows a flow chart of one embodiment of the method according to the present invention for lowering air temperature T_(L) of engine compartment 12 according to FIG. 2. Control unit 42 has an electronic control loop according to the flow chart in FIG. 2, which is provided for activating and deactivating the at least one cooling element 20, 22 in succession to adjust air temperature T_(L) of engine compartment 12 to a setpoint temperature range, an upper temperature of the setpoint temperature range being formed by first limiting value T_(L) ^(max) for air temperature T_(L) of engine compartment 12 of 90° C. and a lower temperature of the setpoint temperature range being formed by second limiting value T_(L) ^(min) for air temperature T_(L) of engine compartment 12 of 70° C.

After an initialization step 52, control unit 42 is put into an operational state. Method steps 54 through 62 which follow are executed in periodic intervals which are clocked by a clock generator of control unit 42.

In another step 54, temperature T_(EA) of electric drive 36 is determined by analysis of a signal of first temperature sensor 48 and air temperature T_(L) of engine compartment 12 by analysis of a signal of second temperature sensor 50. In a next step 56, a first comparative test is carried out between determined temperature T_(EA) of electric drive 36 and limiting value T_(EA) ^(max) stored in memory unit 44 of control unit 42 for a temperature T_(EA) of electric drive 36. If determined temperature T_(EA) of electric drive 36 is greater than stored limiting value T_(EA) ^(max) for a temperature T_(EA) of electric drive 36, then first cooling element 20 and second cooling element 22 are activated in an activation step 60 by starting rotation of the fan and adjusting the flaps into the second position, permitting access of ambient air 24 into engine compartment 12 from outside of engine compartment 12 through the opening formed by the flap. In this way, air temperature T_(L) of engine compartment 12 may be lowered by active purging with ambient air 24, so that a sufficient amount of ambient air 24 at a sufficiently lowered temperature T_(L) may be made available for cooling electric drive 36 in engine compartment 12.

Alternatively, the fan may also be activated as a function of a driving speed of the vehicle in travel direction 10 (not shown in the flow chart) since, due to the inflow of ambient air 24 from outside of engine compartment 12 through the opening formed by the flap, enough ambient air 24 enters engine compartment 12 to cause air temperature T_(L) to be lowered. Activation of the fan could then be stopped above a predetermined driving speed.

If air temperature T_(L) of engine compartment 12 is lowered due to the purging with ambient air 24 to the extent that determined temperature T_(EA) of electric drive 36 is lower than stored limiting value T_(EA) ^(max) for a temperature T_(EA) of electric drive 36, then in a next step 58, a second comparative test between determined air temperature T_(L) and limiting value T_(L) ^(min) stored in memory unit 44 of control unit 42 for an air temperature T_(L) of engine compartment 12 is carried out. As long as determined air temperature T_(L) is higher than stored limiting value T_(L) ^(min) for an air temperature T_(L) of engine compartment 12, first cooling segment 20 and second cooling elements 22 remain in the activated state, i.e., the second position. If determined air temperature T_(L) is at or below stored limiting value T_(L) ^(min) for an air temperature T_(L), then first cooling element 20 and second cooling elements 22 are deactivated in a deactivation step 62 by stopping the rotation of the fan and adjusting the flaps into the first position, in which access of ambient air 24 from outside of engine compartment 12 into engine compartment 12 is prevented by the flap.

In both cases, control unit 42 is provided to activate the at least one cooling element 20, 22, as a function of the temperature of a fluid side of air-fluid heat exchanger 18 and as a function of a temperature T_(EA) of electric drive 36.

In an alternative embodiment, which is represented by dashed lines in FIG. 3, an additional step 57 of a third comparative test may be carried out between step 56 of the first comparative test between determined temperature T_(EA) of electric drive 36 and limiting value T_(EA) ^(max) stored in memory unit 44 of control unit 42, and step 58 of the second comparative test between determined air temperature T_(L) and limiting value T_(L) ^(min) stored in memory unit 44 of control unit 42. In the third comparative test, air temperature T_(L) determined by analysis of a signal of second temperature sensor 50 and first limiting value T_(L) ^(max) stored in memory unit 44 of control unit 42 for an air temperature T_(L) of engine compartment 12 are compared. As long as determined air temperature T_(L) is lower than first limiting value T_(L) ^(max), step 58 of the second comparative test is carried out after the third comparative test. Activation step 60 is carried out after the third comparative test, as soon as determined air temperature T_(L) has reached or exceeded first limiting value T_(L) ^(max). 

What is claimed is:
 1. A method for lowering an air temperature of an engine compartment of a vehicle, the engine compartment accommodating an internal combustion engine, an electric drive, and an air-fluid heat exchanger having at least one cooling element for cooling the air-fluid heat exchanger, the method comprising: activating the at least one cooling element as a function of a temperature of a fluid side of the air-fluid heat exchanger and as a function of a temperature of the electric drive.
 2. The method as recited in claim 1, wherein the at least one cooling element is a fan.
 3. The method as recited in claim 2, wherein a second cooling element in the form of at least one flap is provided, the at least one flap being adjusted by activation from a first position in which an access of ambient air from outside of the engine compartment into the engine compartment is prevented by the flap, into at least one second position in which the access of ambient air from outside of the engine compartment into the engine compartment is enabled through an opening formed by the flap in the second position, the at least one flap being reversibly adjustable between the first position and the second position.
 4. The method as recited in claim 3, wherein the electric drive is operated at an electrical voltage of at most 60 V in a nominal operating range.
 5. The method as recited in claim 4, wherein the electric drive includes an inverter which enables motor operation of the electric drive.
 6. The method as recited in claim 3, wherein the air temperature of the engine compartment is adjusted to a setpoint temperature range by activation of the at least one cooling element in an electronic control circuit.
 7. An electronic control device for lowering an air temperature of an engine compartment of a vehicle, the engine compartment accommodating an internal combustion engine, an electric drive, and an air-fluid heat exchanger having at least one cooling element for cooling the air-fluid heat exchanger, the control device comprising: a control unit configured to selectively activate the at least one cooling element as a function of a temperature of a fluid side of the air-fluid heat exchanger and as a function of a temperature of the electric drive.
 8. The electronic control device as recited in claim 7, wherein the control unit includes at least one electronic control circuit which is provided for selectively activating and deactivating the at least one cooling element in succession to adjust the air temperature of the engine compartment to a setpoint temperature range.
 9. A non-transitory computer-readable data storage medium storing a computer program having program codes which, when executed on a computer, performs a method for lowering an air temperature of an engine compartment of a vehicle, the engine compartment accommodating an internal combustion engine, an electric drive, and an air-fluid heat exchanger having at least one cooling element for cooling the air-fluid heat exchanger, the method comprising: activating the at least one cooling element as a function of a temperature of a fluid side of the air-fluid heat exchanger and as a function of a temperature of the electric drive. 